Đáp án:
`5)x=-13/24`
`6)x=-7/2`
`7)x=-1`
`8)x=-3`
Giải thích các bước giải:
`5)(x-2)³-(x-4)(x²+4x+16)+6(x+1)²=49`
`⇔x³-6x²+12x-8-(x³-64)+6(x²+2x+1)=49`
`⇔x³-6x²+12x-8-x³+64+6x²+12x+6=49`
`⇔(x³-x³)+(-6x²+6x²)+(12x+12x)+(-8+64+6)=49`
`⇔24x+62=49`
`⇔24x=49-62`
`⇔24x=-13`
`⇔x=-13/24`
Vậy `x=-13/24`
`6)(x+2)(x²-2x+4)-x(x²+2)=15`
`⇔x³+8-x³-2x=15`
`⇔-2x+8=15`
`⇔-2x=15-8`
`⇔-2x=7`
`⇔x=-7/2`
Vậy `x=-7/2`
`7)3x(2x-4)-(6x-1)(x+2)=25`
`⇔6x²-12x-(6x²+12x-x-2)=25`
`⇔6x²-12x-6x²-12x+x+2=25`
`⇔(6x²-6x²)+(-12x-12x+x)+2=25`
`⇔-23x+2=25`
`⇔-23x=25-2`
`⇔-23x=23`
`⇔x=23:(-23)`
`⇔x=-1`
Vậy `x=-1`
`8)(x+1)(x+3)-(x+2)(x+5)=2`
`⇔x²+3x+x+3-(x²+5x+2x+10)=2`
`⇔x²+3x+x+3-x²-5x-2x-10=2`
`⇔(x²-x²)+(3x+x-5x-2x)+(3-10)=2`
`⇔-3x-7=2`
`⇔-3x=2+7`
`⇔-3x=9`
`⇔x=9:(-3)`
`⇔x=-3`
Vậy `x=-3`
